Hot Carriers in Quantum Wells for Photovoltaic Efficiency Enhancement

In a hot carrier solar cell, the steady-state carrier population is hot relative to the surrounding lattice. This requires an absorber material which restricts carrier–phonon interaction and, therefore, reduces entropic loss during thermalization. The limiting efficiency of these devices approaches 85%: the Carnot limit for a solar energy collector. A spectroscopic analysis of GaAsP/InGaAs quantum well structures shows that carrier cooling in single quantum well samples is dominated by the rate of radiative recombination, leading to unprecedented carrier cooling lifetime (
$\tau = \hbox{5.8} \pm \hbox{0.1}$
 ns). This exceptional lifetime arises due to state saturation, frustrating the carrier scattering processes. A steady-state carrier population temperature
$>$
100 K above the lattice temperature is measured under illumination equivalent to 10 000 Suns. We calculate the projected efficiency
$>$
40% for a device with these characteristics, amounting to a 3% efficiency enhancement over equivalent single-junction devices.